Light shielding structure of a substrate for a liquid crystal device, liquid crystal device and projection type display device

ABSTRACT

Placement of a first light shielding film ( 7 ) at least below the channel region ( 1   c ) of a TFT which drives a pixel, and of a second light shielding film ( 3 ) above the same prevents impingement of light coming from above or from below on that channel region ( 1   c ) Further, a second light shielding film ( 3 ) is formed to cover the channel region ( 1   c ) and the first light shielding film ( 7 ) thereby to prevent the surface of the first light shielding film ( 7 ) from direct exposure to light

BACKGROUND OF THE INVENTION

[0001] This invention relates to a technique which is suitably adaptedfor production of a substrate for a liquid crystal device, and a liquidcrystal device and projection type display device based on the usethereof. This invention relates more particularly to a light shieldingstructure of the substrate for the liquid crystal device which is usedas a pixel switching element of a thin film transistor (to beabbreviated as TFT hereinafter).

PRIOR ART

[0002] Conventionally, a liquid crystal device is put into practicewhere pixel electrodes have been arranged in the form of a matrix on aglass substrate, and TFTs made of an amorphous silicon film or apolysilicon film have been prepared in correspondence with each pixelelectrode, and which is so constructed as to drive a liquid crystal byapplying a voltage through the TFT to each pixel electrode.

[0003] Among such liquid crystal devices, one incorporating apolysilicon film of which it is possible to assemble peripheral drivingcircuits such as a shift register or the like on the same substratethrough the same process, allows a high density integration of circuitelements and attracts general attention.

[0004] With the liquid crystal device incorporating TFTs, the top of aTFT for driving a pixel electrode (to be referred to as a pixel TFThereinafter) is covered by a light shielding film such as a chromiumfilm called a black matrix (or a black stripe), which is placed on theopposite substrate. This is to prevent the channel region of the TFTfrom being exposed to direct light which would otherwise cause a leakagecurrent. However, a leakage current caused by exposure of the TFT tostray light may arise as a result of light reflected from a polarizerplaced on the back surface of the liquid crystal device, not to mentionthe adverse effects due to incident light itself.

[0005] To minimize such leakage current due to reflective light, aninvention is proposed in which the back: surface of the TFT is alsocovered by a light shielding film (Japanese Patent Publication, No. Hei3-52611). If the light shielding film is placed on the back surface ofthe TFT such that it exceeds in size the opening of the black matrixplaced on the opposite substrate, incident light strikes directly on thelight shielding film, and light reflected therefrom illuminates thechannel region of the TFT, which may cause it to generate a leakagecurrent. This is because, when a process necessary for the placement ofa light shielding film on the back surface of the TFT is put intopractice, precise alignment of a black matrix placed on the oppositematrix with a pixel region placed on the substrate for the liquidcrystal device is difficult, and thus incident light through theopposite substrate directly impinges and is reflected on the part oflight shielding film that exceeds in size the opening of the blackmatrix. As a result, the channel region of TFT is illuminated, causingthe leakage current to flow. Particularly when alignment of the lightshielding layer placed on the substrate for the liquid crystal devicewith the black matrix takes place with a large error, light reflectedfrom the surface of light shielding film increases considerably, and, asthe channel region is illumined by this reflective light, a leakagecurrent from the TFT is increased, resulting in a degraded display as aresult of flaws such as cross-talks or the like.

[0006] The object of this invention is to provide a technique which,when applied to a liquid crystal device, can minimize a leakage currentgenerated from a TFT exposed to light. Another object of this inventionis to provide a technique which can minimize a leakage current from aTFT exposed to light, without resorting to a black matrix placed on theopposite substrate.

DISCLOSURE OF THE INVENTION

[0007] To achieve the above objects, this invention is characterized byproviding a substrate for a liquid crystal device as described in Claim1 comprising:

[0008] a plurality of data lines formed on the substrate;

[0009] a plurality of scan lines crossing the plurality of data lines;

[0010] a plurality of thin film transistors connected to the pluralityof data lines and scan lines; and

[0011] a plurality of pixel electrodes connected to the plurality ofthin film transistors; wherein:

[0012] a first light shielding film formed at least below a channelregion of the thin film transistor, and the junctions between thechannel region and source/drain regions; and

[0013] a second light shielding film formed above the channel region andthe junctions between the channel region and the source/drain regions.

[0014] According to the substrate for a liquid crystal device asdescribed in Claim 1, light impinging from above on the channel regionand on the junctions between the channel region and the source/drainregions is shielded by the first shielding film, and light impingingfrom below is blocked by the second light shielding film. Through thisarrangement, a leakage current which would otherwise be generated in theTFT exposed to light can be stably reduced.

[0015] The substrate for the liquid crystal device as described in Claim2 is characterized in that the first light shielding film may be a metalfilm selected from the group consisting of a tungsten film, titaniumfilm, chromium film, tantalum film and molybdenum film, or an alloy filmthereof.

[0016] According to the substrate for the liquid crystal device asdescribed in Claim 2, when a metal film or a metal alloy film which ishighly impenetrable to light and highly electrically conductive is usedas a first light shielding film, it effectively acts as a lightshielding film against reflective light from the back surface of thesubstrate for the liquid crystal device, and protects the channel regionand the junctions between the channel region and the source/drainregions from exposure to light.

[0017] The substrate for the liquid crystal device as described in Claim3 is characterized in that a first lead extending from the first lightshielding film is electrically connected to a constant potential lineoutside a pixel display region.

[0018] According to the substrate for the liquid crystal device asdescribed in Claim 3, when the first light shielding film is formed in afloating state below the channel region of the TFT, irregular potentialdifferences are generated between different terminals of the TFT, whichmay affect the TFT's performance. As a measure against suchinconvenience, the first light shielding film must be stabilized at aspecific potential level. This is the reason why the first leadextending from the first light shielding film is connected to a linehaving a constant potential such as a ground potential, outside adisplay region. This measure serves for inhibiting generation ofpotential differences among different terminals of the TFT, thuspreventing alteration of TFT performance and occurrence of degradeddisplay quality.

[0019] The substrate for the liquid crystal device as described in Claim4 is characterized in that the first lead extending from the first lightshielding film is formed along and beneath the scan line.

[0020] According to the substrate for the liquid crystal device asdescribed in Claim 4, the first lead extending from the first lightshielding film is formed along and below the scan line. Through thisarrangement it is possible for the lead to run without encroaching theaperture of the pixel. However, the first light shielding film is placedbelow the scan line and is positioned with respect to the side of scanline close to the aperture area of the pixel in such a way as toprohibit the direct impingement of incident light on the surface offirst light shielding film.

[0021] The substrate for the liquid crystal device as described in Claim5 is characterized in that a width of the first lead extending from thefirst light shielding film is less than a width of the scan line formedabove it.

[0022] The substrate for the liquid crystal device as described in Claim6 is characterized in that the first lead extending from the first lightshielding film is covered by the scan line formed above it.

[0023] According to the substrate for the liquid crystal device asdescribed in Claims 5 and 6, the scan line can prevent the first leadextending from the first light shielding film from being directlyexposed to incident light and thus from reflecting incident light.

[0024] The substrate for the liquid crystal device as described in Claim7 is characterized in that a capacitance line which is formed on thesame layer as that of the scan line to add a capacitance to the pixel isplaced in parallel with the scan line, and has below it a second leadextending from the first light shielding film.

[0025] According to the substrate for the liquid crystal device asdescribed in Claim 7, the second line extending from the first lightshielding film, by being placed below the capacitance line which runsparallel with the scan line, and an added capacitor is formed by thesecond line, the drain region of the TFT and a first interlevelinsulating film as a dielectric material. Through this arrangement it ispossible to increase an extra capacitance without reducing the apertureof the pixel.

[0026] The substrate for the liquid crystal device as described in Claim8 is characterized in that a third lead extending from the first lightshielding film is placed along and below a data line.

[0027] According to the substrate for the liquid crystal device asdescribed in Claim 8, the third lead extending from the first lightshielding film may be formed along and below the data line. This leadextension, however, should be arranged such that the first lightshielding film placed below the data line is covered by the data line atthe areas where the data line comes into contact with or comes veryclose to the pixel aperture region, in order to prevent the surface ofthe first light shielding film from being directly exposed to incidentlight.

[0028] The substrate for the liquid crystal device as described in Claim9 is characterized in that the data line also acts as a second lightshielding film, and is made of any metal film selected from an aluminumfilm, tungsten film, titanium film, chromium film, tantalum film andmolybdenum film, or an alloy film thereof.

[0029] According to the substrate for the liquid crystal device asdescribed in Claim 9, preparing the data line from a metal film or ametal alloy film makes it possible for the data line to also act as asecond light shielding film. This arrangement makes it unnecessary toprepare a layer only for light shielding.

[0030] The substrate for the liquid crystal device as described in Claim10 is characterized in that the third lead extending from the firstlight shielding film has a smaller width than that of data line.

[0031] The substrate for the liquid crystal device as described in Claim11 is characterized in that the channel region and the junction betweenthe channel region forms and the source/drain region are placed beneaththe data line, and that the first light shielding film placed beneaththe channel region and the junction between the channel region and thesource/drain region is covered by the data line at least on the partunderlying the channel region and the junction between the channelregion forms and the source/drain region.

[0032] According to the substrate for the liquid crystal device asdescribed in Claim 11, at least the channel region and the junctionsbetween the channel region and the source/drain regions are shielded bythe data line (second light shielding film) from exposure to incidentlight from above. When incident light comes from above, it is necessaryto protect the channel region and the junctions between the channelregion and the source/drain regions from exposure to light reflectedfrom the surface of the first light shielding film. To achieve this, thedata line is formed in such a way as to totally cover the first lightshielding film placed beneath the channel region and the junctionsbetween the channel region and the source/drain regions.

[0033] The substrate for the liquid crystal device as described in Claim12 is characterized in that LDD regions are formed at the junctionsbetween the channel region and the source/drain regions.

[0034] According to the substrate for the liquid crystal device asdescribed in Claim 12, the junctions of the channel region withsource/drain regions of a pixel TFT are prepared as LDD regions, whichenables the reduction of a leakage current which would otherwise resultwhen the TFT is turned off. However, when the LDD region is exposed tolight, generally electrons within are readily excited. Thus, it isnecessary to cover the LDD region with the first and second lightshielding films from above and below, as is the case with the channelregion.

[0035] The substrate for the liquid crystal device as described in Claim13 is characterized in that the junctions between the channel region andthe source/drain regions are formed as offset regions.

[0036] According to the substrate for the liquid crystal device asdescribed in Claim 13, the junctions between the channel region of thepixel TFT and the source/drain regions are formed as offset regions notdoped with impurity ions, which enables the reduction of a leakagecurrent which would otherwise result when the TFT is turned off.However, when the offset region is exposed to light, generally electronswithin are readily excited as in the LDD region. Therefore, like thechannel region, the offset regions are so formed as to be totallycovered by the first and second light shielding films from above andbelow.

[0037] The substrate for the liquid crystal device as described above inClaim 14 is characterized in that the scan line is made of any metalfilm selected from a tungsten film, titanium film, chromium film,tantalum film and molybdenum film, or of a metal alloy film thereof.

[0038] According to the substrate for the liquid crystal device asdescribed in Claim 14, the scan line is made at least of a metal film ora metal alloy film which makes it possible for the scan line to also actas a light shielding film. Because through this arrangement it ispossible for the scan line as well as the data line to act as a lightshielding film, placement of a black matrix on the opposite substratecan be safely omitted, by forming all the sides surrounding the pixelelectrode so as to overlap with the data lines and the scan lines.

[0039] The substrate for the liquid crystal device as described in Claim15 is characterized in that the smallest distance L1 from the lateraledges of first light shielding film to the channel region is made 0.2μm≦L1≦4 μm.

[0040] According to the substrate for the liquid crystal device asdescribed in Claim 15, it is possible to prevent adverse effects due toreflective light from the first light shielding film.

[0041] The substrate for the liquid crystal device as described in Claim16 is characterized in that the smallest distance L2 from the lateraledges of the second light shielding film to the lateral edges of firstlight shielding film is made 0.2 μm ≦L2.

[0042] According to the substrate for the liquid crystal device asdescribed in Claim 16, it is possible to prevent adverse effects due toreflective light from the first light shielding film.

[0043] The substrate for the liquid crystal device as described in Claim17 is characterized in that the substrate for the liquid crystal deviceand an opposite substrate with an opposite electrode are placed with aspecified interval in between, and that liquid crystal is inserted intothe space between the substrate for the liquid crystal device and theopposite substrate.

[0044] According to the substrate for the liquid crystal device asdescribed in Claim 17, the substrate for the liquid crystal device andthe opposite substrate are bonded together by a specified cell gap,liquid crystal is injected into the space between the substrate for theliquid crystal device and the opposite substrate, and a voltage isapplied across the liquid crystal to achieve a gray scale. This liquidcrystal device, as long as it receives incident light only through theopposite substrate, ensures a high grade display of images free fromadverse effects due to stray light.

[0045] The liquid crystal device as described in Claim 18 ischaracterized in that a third light shielding film is formed on theopposite substrate.

[0046] According to the liquid crystal device as described in Claim 18,on the opposite substrate is formed a black matrix (third lightshielding film) with a high light shielding property which is made of ametal film such as chromium film or a black matrix composed of anorganic substance. The pixel TFT placed on the substrate for the liquidcrystal device is prevented by the black matrix from being directlyexposed to light. This arrangement makes it possible to provide a liquidcrystal device with a display capable of reproducing high qualityimages.

[0047] The liquid crystal device as described in Claim 19 ischaracterized in that the third light shielding film covers at least thefirst light shielding film.

[0048] According to the liquid crystal device as described in Claim 19,the first light shielding film placed on the substrate for the liquidcrystal device is covered by the black matrix (third light shieldingfilm) on the opposite substrate, which makes it possible for the firstlight shielding film to be shielded from direct exposure to incidentlight. This arrangement prevents light reflected from the surface oflight shielding film from impinging on the channel region of the TFT andthe junctions between the channel region and the source/drain regions,which enables the reduction of a leakage current which would otherwisearise if the TFT were exposed to light.

[0049] The liquid crystal device as described in Claim 20 ischaracterized in that small lenses are arranged in the form of a matrixon the opposite electrode in correspondence with the plurality of pixelelectrodes placed on the substrate for the liquid crystal displaydevice.

[0050] According to the liquid crystal device as described in Claim 20,the small lens mounted on the opposite electrode converges light ontothe pixel aperture region on the substrate for the liquid crystaldevice. The first light shielding film is placed on the substrate forthe liquid crystal device such that light converged by the small lens,even when reflected from the back surface of the substrate for theliquid crystal device, is prevented from impinging on the channel regionof the pixel TFT. Accordingly, even when light is converged by the smalllens into a strong flux, it does not affect the TFT performance, andthus production of a liquid crystal device capable of reproducingbright, high quality images will be ensured.

[0051] The projection type display system as described in Claim 21 ischaracterized by comprising a light source, a liquid crystal device totransmit or reflect light from the light source, after having modulatedit, and an optical projection means which receives the modulated lightsent from the liquid crystal device, and converges and enlarges itthrough projection.

[0052] According to the projection type display system as described inClaim 21, the projection type display system has a liquid crystal deviceof this invention, and can prevent the entry of stray light through thefirst light shielding film on the substrate for the liquid crystaldevice, even when the back surface of the substrate for the liquidcrystal device is exposed to such light as reflected from a dichroicprism or the like. Accordingly, even when light is intensified and suchintensified light is incident on the liquid crystal device, it does notaffect the TFT performance, and thus production of a projection typedisplay system capable of reproducing bright, high quality images willbe ensured.

[0053] Operation and other advantages of this invention will be clearlydescribed with reference to preferred embodiments given below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0054]FIG. 1 is a plan view of pixels which represent the firstembodiment of a substrate for a liquid crystal device to which thisinvention has been applied.

[0055]FIG. 2 is a sectional view of a pixel cut along the line A-A′ ofFIG. 1.

[0056]FIG. 3 is a series of sectional views illustrating the processes(front half) necessary for production of a substrate for a liquidcrystal device of the first embodiment which are arranged in order.

[0057]FIG. 4 is a series of sectional views illustrating the processes(rear half) necessary for production of a substrate for a liquid crystaldevice of the first embodiment which are arranged in order.

[0058]FIG. 5 is a plan view of pixels which represent the secondembodiment of a substrate for a liquid crystal device to which thisinvention has been applied.

[0059]FIG. 6 is a sectional view of a pixel cut along the line B-B′ ofFIG. 1.

[0060]FIG. 7 is a plan view of pixels which represent the thirdembodiment of a substrate for a liquid crystal device to which thisinvention has been applied.

[0061]FIG. 8 is a sectional view of a pixel cut along the line C-C′ ofFIG. 7.

[0062]FIG. 9 is a plan view of pixels which represent the fourthembodiment of a substrate for a liquid crystal device to which thisinvention has been applied.

[0063]FIG. 10 is a sectional view of a pixel cut along the line D-D′ ofFIG. 9.

[0064]FIG. 11 is a plan view of pixels which represent the fifthembodiment of a substrate for a liquid crystal device to which thisinvention has been applied.

[0065]FIG. 12 is a plan view of pixels which represent the sixthembodiment of a substrate for a liquid crystal device to which thisinvention has been applied.

[0066]FIG. 13 is a plan view of pixels which represent the seventhembodiment of a substrate for a liquid crystal device to which thisinvention has been applied.

[0067]FIG. 14 is a sectional view of a pixel cut along the line E-E′ ofFIG. 13.

[0068]FIG. 15 is a block diagram illustrating the constitution of asubstrate for a liquid crystal device to which this invention ispreferably applied.

[0069]FIG. 16 gives a plan view (a) and a sectional view along line H-H′of a liquid crystal device incorporating a substrate for liquid crystaldevice prepared according to this invention

[0070]FIG. 17 is a schematic diagram outlining the constitution of aliquid crystal projector presented as an embodiment of a projection typedisplay system which incorporates as a light valve a liquid crystaldevice containing a substrate for a liquid crystal device preparedaccording to this invention.

[0071]FIG. 18 is a sectional view of a liquid crystal device whichincorporates small lenses on the opposite substrate to illustrate theconstitution thereof.

[0072]FIG. 19 is a plan view of pixels which represent the eighthembodiment of a substrate for a liquid crystal device to which thisinvention has been applied.

[0073]FIG. 20 is a sectional view of a pixel cut along the line F-F′ ofFIG. 19.

[0074]1: Semiconductor layer

[0075]2: Scan line (gate electrode)

[0076]3: Data line (second light shielding film)

[0077]4: Contact hole connecting pixel electrode and drain region

[0078]5: Contact hole connecting data line and source region

[0079]6: Black matrix on the opposite substrate (third light shieldingfilm)

[0080]7: First light shielding film

[0081]10: Substrate

[0082]11: First interlevel insulating film

[0083]12: Gate insulating film

[0084]13: Second interlevel insulating film

[0085]14: Pixel electrode

[0086]15: Third interlevel insulating film

[0087]16: Capacitance line

[0088]17: Resistor mask

[0089]20: Display region

[0090]30: Liquid crystal device

[0091]31: Opposite substrate

[0092]32: Substrate for liquid crystal device

[0093]33: Opposite electrode

[0094]36: Sealing layer

[0095]37: Liquid crystal

[0096]38: Injection port of liquid crystal

[0097]39: Sealing material

[0098]40: Input/output terminals

[0099]50: Data line driving circuit

[0100]51: X shift register

[0101]52: Sampling switch

[0102]53: X buffer

[0103]54-56: Image signal lines

[0104]60: Scan line driving circuit

[0105]61: Y shift register

[0106]63: Y buffer

[0107]80: Small lens

[0108]90: Pixel

[0109]91: Pixel TFT

[0110]370: Light source

[0111]373, 375, 376: Dichroic mirror

[0112]374, 377: Reflection mirror

[0113]378, 379, 380: Light valve

[0114]383: Dichroic prism

[0115]384: Projection lens

DESCRIPTION OF THE BEST MODE

[0116] Preferred embodiments of this invention will be described belowwith reference to attached figures.

[0117] (Embodiment 1)

[0118]FIGS. 1 and 2 represent the first preferred embodiment of asubstrate for a liquid crystal device to which this invention has beenapplied. FIG. 1 is a plan view of pixels arrayed side by side, whileFIG. 2 is a sectional view of the same along line A-A′ of FIG. 1, thatis, a cross-section of a semiconductor layer 1 which serves as an activelayer of a TFT.

[0119] In FIG. 1, 1 represents a polysilicon film which forms a firstlayer of the semiconductor layer of the TFT, and, on the surface ofsemiconductor layer 1 is formed a gate insulating film 12 which has beenproduced by thermal oxidation, as shown in FIG. 2. Scan lines 2 act ascommon gate electrodes to TFTs arrayed in the same column (arrayedcrosswise in the figure), 3 represents a data line which is so placedlengthwise as to intersect the scan line 2 at right angles, and isintroduced to provide a voltage to the source regions of the TFTsarrayed in a vertical direction along the same row. The scan line 2 ismade of a polysilicon film which forms a second layer, and the data line3 is made of an electroconductive layer such as an aluminum film.

[0120] Further, 4 represents a contact hole which is to connect a pixelelectrode 14 made of an electroconductive layer such as an ITO film andthe drain region of the first semiconductor layer 1 of the TFT, and 5represents another contact hole which is to connect the data line 3 andthe source region of first semiconductor layer 1 of the TFT. A blackmatrix 6 (third light shielding film) is implemented on an oppositesubstrate 31 to face the scan line 2 and data line 3, and consists of ametal film such as a chromium film or a black organic film or the like.

[0121] In this first embodiment, below the semiconductor layer 1 whichacts as an active layer of the TFT, particularly below a channel region1 c (an area shaded with parallel lines with a negative gradient in FIG.1), and junctions between LDD regions (or offset regions) 1 d and 1 e,and source/drain regions 1 a and 1 b, and the scan line 2, is placed afirst light shielding film 7 (an area shaded with parallel lines with apositive gradient in FIG. 1) which is made of a metal such as tungsten,titanium, chromium, tantalum or molybdenum, or their alloy. As isevident from above, the semiconductor layer 1 is inserted between thefirst light shielding film 7 on one hand, and the second light shieldingfilm (data line) 3 and the third light shielding film (black matrix) 6on the other, and sandwiched from above and below with those films.Therefore, not only incident light from above but light reflected fromthe back surface of the substrate for the liquid crystal device can beprevented from impinging on the elements of the TFT, particularly on thechannel region 1 c, and the junctions between LDD regions 1 d and 1 e(or offset regions) and source/drain regions 1 a and 1 b. Thus,generation of a leakage current can be successfully suppressed.Furthermore, even if, when the substrate for the liquid crystal deviceand the opposite substrate are bonded together, alignment of the displayregion of the substrate for the liquid crystal device with respect tothe black matrix 6 (third light shielding film) on the oppositesubstrate 31 takes place with a more or less error, incident light willnot directly impinge on the channel region 1 c and LDD regions 1 d and 1e (or offset regions) of the TFT, and on the first light shielding film7, because the channel region 1 c and LDD regions 1 d and 1 e (or offsetregions) of the TFT are masked with the second light shielding film 3(data line). This arrangement allows a great reduction of leakagecurrent which would be otherwise generated in the TFT exposed to straylight.

[0122] The reason why the first light shielding film 7 is extended sofar as to underlie the scan line 2 is to provide the first lightshielding film 7 just beneath the channel region 1 c which absolutelydemands light shielding, with a constant potential like a groundpotential, thereby keeping the first light shielding film 7 from takinga floating state. This arrangement prevents fluctuations of TFTperformance. The constant potential may be connected to a constantpotential line (not illustrated here) such as a negative power sourcewhich is connected to a peripheral driving circuit mounted on the samesubstrate through the same process responsible for the formation ofpixels. Particularly when the constant potential is so chosen as to givethe same low level voltage with that of a gate signal provided to thescan line 2, it will prevent the occurrence of fluctuations in TFTperformance. As seen from the context of the above discussion, it ismost effective to electrically connect the shielding film in question toa negative power source (not illustrated here) of a scan line drivingcircuit to activate the scan line 2.

[0123] Further, the first light shielding film below the scan line 2 ispreferably placed, with respect to the side of scan line 2 close to apixel aperture, below the inside of scan line 2 rather than below theside of the same line 2. Through this arrangement it becomes possible toprevent the occurrence of light reflection from the first lightshielding film 7 below the scan line 2. Furthermore, the first lightshielding film 7 is preferably treated with an oxidative agent to give asurface sufficiently rough to diffuse reflective light, or is made of apolysilicon film, thereby preventing the occurrence of reflective light.

[0124] In this first embodiment, at least the channel region 1 c, andLDD regions (or offset regions) 1 d and 1 e of the TFT are placed belowthe data line 3 (second light shielding film). Hence, as the channelregion 1 c is completely covered by the data line 3 (second lightshielding film), direct impingement of incident light an the channelregion 1 c can be securely prevented.

[0125] In Embodiment 1, though not being restrictive, to efficientlyconfer an extra capacitance to the drain of the TFT, the channel region1 c of the first layer of semiconductor layer 1 takes a course asindicated by symbol 1 f: it extends above along the data line 3, andflexes towards its own pixel electrode 14 along the scan line 2 of thepixel of the foregoing array (upper array in FIG. 1). Then, a part ofscan line 2 of the foregoing array is allowed to take a downward coursesimilarly to above along the data line 3 as indicated by symbol 2 f.Through this arrangement, a capacitance (with the gate insulating film12 as a dielectric body) between the extension 1 f of the first layer ofsemiconductor layer 1 and the extension 2 f of scan line 2 is connectedas an extra capacitance to the drain of the TFT which gives a voltage toindividual pixel electrodes 14. The thus added extra capacitance canminimize the adverse effects of input voltage alterations on the pixelaperture. Accordingly, with this arrangement, it is possible not only tomaintain the pixel aperture at a high level, but to obtain an increasedextra capacitance.

[0126] Next, by means of FIG. 2 which gives a sectional view of thesemiconductor layer 1 approximately representing its profile from thecontact hole 4 to contact hole 5 of FIG. 1, the sectional structure ofpixel TFT of this invention will be described in detail. A substrate 10is made of non-alkali glass or quartz, 11 is a first interlevelinsulating film inserted between the TFT semiconductor layer 1 and firstlight shielding film 7, and made of a silicon oxide or silicon nitridefilm, and has been prepared by high pressure CVD or the like. Further,12 is a gate insulating film, 13 a second interlevel insulating film, 15a third interlevel insulating film and 14 is a pixel electrode made ofan ITO film or the like.

[0127] In this first embodiment, the TFT as a switching element of thepixel has an LDD structure (or offset structure). Namely, thesource/drain region consists of LDD regions (or offset regions) 1 d and1 e, and source/drain regions 1 a and 1 b. Below the gate electrode 2 ispositioned a channel region 1 c. As is evident from FIG. 2, part ofdrain region 1 b is not covered by the first light shielding layer 7,and hence the semiconductor layer 1 has a step at a junction where aportion covered by the first light shielding layer 7 comes into contactwith the remaining portion which is not covered by the first lightshielding layer 7. As this step is several microns apart from thejunction between the drain region 1 b and LDD region 1 e, or, as thisstep is several microns apart from the junction in question towards thedrain, the existence of this step does not affect the performance of theTFT. By allowing the TFT to have an LDD structure or an offsetstructure, it is possible to further reduce a leakage current generatedduring the switching-off of the TFT which would otherwise becomeconsiderable. Although the TFT described above is assumed to have an LDDstructure (or offset structure), of course it may have a self-alignedstructure which forms source and drain regions in a self-aligned mannerwith the gate electrode 2 as a mask.

[0128] Further, according to this first embodiment, the first lightshielding film 7 is so formed as to cover from below the source/drainregions 1 a and 1 b, and junctions between channel region 1 c and LDDregions (or offset regions) of semiconductor layer 1, and the data line3 (second light shielding film) is also so formed as to cover from abovethe channel region 1 c and LDD regions 1 d and 1 e (or offset regions).Therefore, the channel region 1 c and LDD regions 1 d and 1 e (or offsetregions) are covered doubly from light, that is, from incident lightcoming from above and reflective light coming from below. Furthermore,as the data line 3 (second light shielding film) covers from above thefirst light shielding film 7 at regions where the data line 3 runs incontact with or very close to the pixel aperture area, it is possible toprevent the reflection of incident light from the surface of firstshielding film 7

[0129] In addition to above, because a black matrix 6 (third lightshielding film) coated on the opposite electrode 31 is so formed as tocover from above the channel region 1 c and LDD regions 1 d and 1 e (oroffset regions), light shielding of the channel region 1 c and LDDregions 1 d and 1 e (or offset regions) is further strengthened. Inaddition, because the black matrix 6 (third light shielding film) coversthe first light shielding film 7 with ample margins, it furthereffectively prevents direct impingement of incident light on the firstlight shielding film. Accordingly, with a liquid crystal deviceincorporating a substrate for the liquid crystal device of thisinvention, incident light is prevented from being reflected from thefirst light shielding film 7 and from impinging on the channel region 1c and LDD regions 1 d and 1 e (or offset regions), and hence it ispossible to minimize a leakage current of the TFT which otherwise wouldbe generated if it were exposed to stray light. Thus, such device canpresent a display of high quality images free from image degradingeffects such as cross-talk.

[0130] (Production Process)

[0131] Next, by means of FIGS. 3 and 4, the production process of thisinvention will be described. First, on a substrate 10 made of non-alkaliglass or quartz is formed by sputtering or the like an electroconductivefilm such as a tungsten film, a titanium film, a chromium film, atantalum film, or a molybdenum film or an alloy film such as metalsilicide with a thickness of about 500-3,000 Å, or more preferably1,000-2,000 Å. Then, a pattern is printed thereupon by photolithographyor photoetching to form the first light shielding film 7 (FIG. 3a) Thisfirst light shielding film 7 is so formed as to cover from below atleast the channel region 1 c and LDD regions 1 d and 1 e (or offsetregions) of the TFT which is to be produced in a later process. Thefirst light shielding film may be a film made of an organic substance aslong as it absorbs incident light. Further, in order to prevent thefirst light shielding film 7 from giving from its surface a strongreflective ray, the surface of first light shielding film 7 may besubmitted to an oxidation treatment to become rough and thus to dispersereflective light diffusely. Alternatively, the first light shieldingfilm 7 may have a double-layered structure by having another layer ofpolysilicon coated on the first film so that incident light may beabsorbed by the polysilicon film.

[0132] Then, on the first light shielding film 7 is formed the firstinterlevel insulating film 11 so as to have a thickness of about1,000-15,000 Å, or more preferably 5,000-10,000 Å (FIG. 3b). The firstinterlevel insulating film 11 is to insulate the first insulating film 7from the semiconductor layer 1, and is formed by normal pressure CVD orby TEOS gas method and composed of a silicon oxide film or a siliconnitride film.

[0133] Following the formation of first interlevel insulating film 11,while the substrate 10 is being heated at about 500° C., monosilane gasor disilane gas is supplied at a flow rate of about 400-600 cc/min undera pressure of about 20-40 Pa to form an amorphous silicon film on thefirst interlevel insulating film 11. Then, it is subjected to annealingat the temperature of about 600 to 700° C. for about 1 to 72 hours underN₂ atmosphere and is grown in fixed phase to form a polysilicon film.

[0134] Later, photolithography or photoetching technique is applied tocomplete the semiconductor layer 1 of the TFT (FIG. 3c) This polysiliconfilm may be prepared by reduced pressure CVD or the like to have athickness of about 500-2,000 Å, or more preferably about 1,000 Å, or itmay be produced after a polysilicon layer deposited by reduced pressureCVD has been doped with silicon ions to be turned in an amorphoussubstance which is then recrystallized by annealing.

[0135] Next, the semiconductor layer 1 is oxidized by heating, toproduce a semiconductor 1 overlaid with the gate insulating electrode 12(FIG. 3d). Through this process, the semiconductor layer finally comesto have a thickness of 300-1,500 Å, more preferably about 350-450 Åwhile the gate insulating film comes to have a thickness of about600-1,500 Å. Incidentally, when a substrate as large as an eight inchdisplay is produced, to prevent the bending of the substrate duringheating, the time for thermal oxidation is preferably shortened to allowthe formation of a thin oxide film, upon which a high temperaturesilicon oxide film (HTO film) or a silicon nitrate film is deposited byCVD or the like, to form a laminar structure comprising two or morelayers to act as an insulating film. The portion of the semiconductorlayer made of polysilicon which extends upwards along the data line 3 toadd an extra capacitance (If in FIG. 1) is doped with an impurity suchas phosphor at a dose of 3×10¹²/cm², to reduce the resistance thereof.The lower limit of the dose can be determined by how much of theimpurity is necessary to confer a necessary electroconductivity to allowa sufficient extra capacitance. On the other hand, the upper limit isdetermined by how much of the impurity is necessary for preventingdegradation of the gate insulating film 12.

[0136] Next, a polysilicon film which acts as the gate electrode andscan line 2 is deposited on the semiconductor 1 with the gate insulatingfilm 12 inserted in between, and a pattern is printed thereupon byphotolithography or a photoetching technique (FIG. 3e). The gateelectrode may be made of a polysilicon film or of a film made of amaterial capable of shielding light, that is, an electroconductive metalfilm such as a tungsten film, a titanium film, a chromium film, atantalum film, a molybdenum film, or an alloy film such as metalsilicide. Then, as it effectively prevents the entry of incident lightto the channel region 1 and LDD regions 1 d and 1 e (or offset regions),the light shielding effect of the device is further improved. As thisarrangement dispenses with the coating of black matrix 6 (third lightshielding film) on the opposite matrix 31, it becomes possible toprevent the reduction of transmittance of the liquid crystal devicewhich may result from imprecise bonding of the opposite substrate 31 tothe substrate for the liquid crystal device.

[0137] Next, to form an N-channel TFT, impurity ions (e.g., phosphorions) are implanted at a dose of about 0.1−10×10¹³/cm² with the gateelectrode 2 as a mask to form low-density regions (LDD regions) 1 d and1 e (FIG. 3f)

[0138] Further, a resist mask 17 having a larger width than that of gateelectrode 2 is formed over the gate electrode 2, and impurity ions(e.g., phosphor ions) are implanted at a dose of about 0.1−10×10¹³/cm²(FIG. 4g). Through this procedure, the masked regions become LDDregions. Namely, LDD regions 1 d and 1 e, and source/drain regions 1 aand 1 b are formed, and the channel region 1 c is formed beneath thegate electrode 2. As is evident from above, when ions are implanted, thepolysilicon film to act as the gate electrode 2 (scan line) is alsodoped with the impurity ions, and hence has its resistance reduced.Instead of practicing the above process for introducing impurity ions,that is, instead of implanting a low concentration of impurity ions(e.g., phosphor ions), the resist mask 17 having a larger width thanthat of gate electrode 2 is formed over the gate electrode 2 and a highconcentration of impurity ions (e.g., phosphor ions) may be implanted toform N-channel source/drain regions 1 a, 1 b. Alternatively, a highconcentration of impurity ions (e.g., phosphor ions) may be implantedwith the gate electrode 2 as a mask to form n-channel source/drainregions with a self-aligning structure.

[0139] Further, though not illustrated here, to form a p-channel TFT ofa peripheral driving circuit, the pixel TFT and N-channel TFT arecovered with a resistor film for protection, and impurity ions (e.g.,boron ions) are implanted at a dose of about 0.1−10×10¹³/cm² with thegate electrode 2 as a mask, to produce low density regions 1 d and 1 e(LDD regions).

[0140] Furthermore, a resist mask 17 having a larger width than that ofgate electrode 2 is formed over the gate electrode 2, and impurity ions(e.g., boron ions) are implanted at a dose of about 0.1−10×10¹³/cm²(FIG. 4g). Through this procedure, the masked regions come to have alightly doped drain (LDD) structure. Namely, LDD regions 1 d and 1 e,and source/drain regions 1 a and 1 b are formed, and the channel region1 c is formed beneath the gate electrode 2.

[0141] Instead of practicing the above process for introducing impurityions, that is, instead of implanting a low concentration of impurityions (e.g., boron ions), the resist mask 17 having a larger width thanthat of gate electrode 2 is allowed to form over the gate electrode 2,and a high concentration of impurity ions (e.g., boron ions) may beimplanted to form P-channel source/drain regions with an offsetstructure. Alternatively, with the gate electrode 2 as a mask, a highconcentration of impurity ions (e.g., boron ions) may be implanted toform N-channel source/drain regions with a self-aligned structure.Through these ion implantation processes, it is possible to produce aCMOS (complimentary MOS) TFT, and to build peripheral driving circuitstogether with pixel TFTs on the same substrate as the pixel TFT.

[0142] Later, the second interlevel insulating film 13 made of a siliconoxide film or a silicon nitride film is formed, for embodiment, by CVDover the whole surface of substrate 10 to cover the gate electrode 2with a thickness of 5,000-15,000 Å. The second interlevel insulatingfilm 13 is made of a silicon oxide film (NSG) or a silicon nitride filmfree from boron or phosphor. Then, after annealing to activate thesource/drain regions, through the second interlevel insulating film 13is opened a contact hole 5 by dry etching or the like which correspondsin position with the source region 1 a of TFT. Then, by sputtering orthe like, a metal film such as an aluminum film, a titanium film, atungsten film, a tantalum film, a chromium film, a molybdenum film,etc., or an alloy film is formed thereupon so as to have a thickness of,for embodiment, 2,000-6,000 Å, which is then processed by aphotolithography or etching techniques to give a patterning to the dataline (second light shielding film). During this process, the data line 3(second light shielding film) is connected to the semiconductor layer 1(FIG. 4h) through the contact hole 5. In this process, the data line 3(second light shielding film) is allowed to cover at least the channelregion 1 c and LOD regions 1 d and 1 e (or offset regions).

[0143] Then, the third interlevel insulating film 15 is formed, forembodiment, by CVD or normal pressure ozone TEOS over the whole surfaceof substrate 10 as if to cover the data line 3 with a thickness of5,000-15,000 Å. The third interlevel insulating film 15 is made of asilicon oxide film (BPSG) or a silicon nitride film containing boron andphosphor. Or, it may have another coat made of an organic substanceadded using a spin coater to smooth its surface to be free from steps.When the above smoothing treatment is introduced during the formation ofthe third interlevel insulating film or a process just prior to theformation of pixel electrode 14, it is possible to minimize a loweringin contrast due to inappropriate arrangement of liquid crystalmolecules. Then, through the third interlevel insulating film 15 isopened a contact hole 4 by dry etching or the like which contacts withthe drain region 1 b of the pixel TFT, and the pixel electrode 14 whichis formed later is connected through this contact hole 4 to thesemiconductor layer 1 (FIG. 4i).

[0144] The pixel electrode 14 is obtained after an ITO film has beenformed by sputtering or the like so as to have a thickness of 400-2,000Å, and is subjected to a patterning by a photolithography or etchingtechnique. Then, an alignment film made of polyimide or the like iscovered over the pixel electrode 14 and a third interlevel insulatingfilm 15 so as to have a thickness of about 200-1,000 Å over the wholesurface of substrate 10, and a rubbing (aligning treatment) is appliedon the surface thereof to produce the substrate for liquid crystaldevice.

[0145] In embodiment 1, description has been made assuming that the TFThas an LDD structure, but it may have an offset structure, or it mayhave a self-aligned structure with the gate electrode as a mask. To letthe TFT have an offset structure, the process depicted in FIG. 4f may beomitted. To let the TFT have a self-aligned structure, a highconcentration of impurities are implanted during the process as depictedin FIG. 4f, and the process of FIG. 4g should be omitted.

[0146] (Embodiment 2)

[0147]FIGS. 5 and 6 represent the second preferred embodiment of asubstrate for a liquid crystal device to which this invention has beenapplied. FIG. 5 is a plan view of pixels arrayed side by side, whileFIG. 6 is a sectional view of the same along line B-B′ of FIG. 5, thatis, a cross-section of a semiconductor layer 1 which serves as an activelayer of the TFT. In embodiment 2, below the semiconductor layer 1 andscan line 2 is formed a first light shielding film 7 (areas shaded withparallel lines with a positive gradient in FIG. 5), and thesemiconductor layer 1 is so prepared with respect to the scan line 2 asto intersect the latter two times within a pixel unit. Through thisarrangement, it is possible to maintain the distance of the channelregion 1 c of pixel TFT from both contact holes constant even if thescan line 2 (gate electrode) (areas shaded with parallel lines with anegative gradient in FIG. 5) is displaced with respect to thesemiconductor layer 1, and thus a lowering in display quality whichwould otherwise result can be effectively prevented. Further, for agiven pixel, the semiconductor layer 1 to provide the channel region 1 cof pixel TFT intersects twice with the scan line 2, and the channelregions 1 c formed at those intersections are connected in series.Therefore, the resistance component of the pixel TFT is increased, whichcontributes to a lowering of the leakage current which would otherwiseoccur when the TFT is switched off.

[0148] Also in embodiment 2, the pixel TFT may have an LDD structure oran offset structure. It will be possible to further lessen the leakagecurrent if the pixel TFT has an LDD structure or an offset structure, inaddition to a dual gate structure or a triple gate structure. Further,in embodiment 2, one of two pairs of channel regions 1 c and LDD regions1 d and 1 e (left pair of FIG. 5) is placed beneath a data line 3(second light shielding film) made of an aluminum film. Through thisarrangement, it is possible for the data line 3 (second light shieldingfilm) to act as a shielding film against incident light from above orlight coming from the side where an opposite substrate 31 resides, andthus to prevent the light from directly impinging on the channel region1 c and LDD regions 1 d and 1 e (or offset regions) of the pixel TFT.Therefore, the leakage current can further be reduced. This contributesto further lessen the leakage current. In this arrangement, however, itis possible for the channel region 1 c and LDD regions (or offsetregions) (right pair of FIG. 5) which are not covered by the data line 3(second light shielding film) to be exposed to incident light.Nevertheless, because at least one of two channel regions connected inseries is free from adverse effects due to stray light, no leakagecurrent as a result of stray light would ensue, and further the TFT,having a dual gate structure, will give a lowered resistance whenswitched off.

[0149] In embodiment 2 like embodiment 1, the first light shielding film7 is prepared smaller in size than a black matrix formed on an oppositesubstrate 31. Accordingly, incident light is prevented from impingingdirectly on the surface of first light shielding film 7, and thusgeneration of leakage current due to light reflected from the firstlight shielding film 7 can be effectively suppressed. Further, the firstlight shielding film 7 is so prepared as to have a smaller width thandoes the scan line 2, thereby preventing direct impingement of incidentlight on the first light shielding film 7 which extends below the scanline 2 in the same direction.

[0150] In embodiment 1, though not being restrictive, to effectivelyconfer an extra capacitance to the drain of the TFT, the channel region1 c of the first layer of semiconductor layer 1 takes a course asindicated by symbol if: it extends above along the data line 3, andflexes towards an adjacent pixel electrode 14 (of the left adjacentpixel in FIG. 5) along the scan line 2 of the pixel of the foregoingarray (upper array in FIG. 5). Then, a part of scan line 2 of theforegoing array is allowed to take a downward course along the data line3 as indicated by symbol 2 f. Through this arrangement, a capacitance(with the gate insulating film 12 as a dielectric body) between theextension 1 f of the first layer of semiconductor layer 1 and theextension 2 f of scan line 2 is connected as an extra capacitance to thedrain of the TFT which gives a voltage to individual pixel electrodes 14The thus added extra capacitance can minimize the adverse effects ofinput voltage changes on the pixel aperture. Accordingly, with thisarrangement, it is possible not only to maintain the pixel aperture at ahigh level, but to obtain an increased extra capacitance.

[0151] Further, embodiment 2 can be produced through the same productionprocesses as used for the production of embodiment 1.

[0152] (Embodiment 3)

[0153]FIGS. 7 and 8 represent the third preferred embodiment of asubstrate for a liquid crystal device to which this invention has beenapplied. FIG. 7 is a plan view of pixels arrayed side by side, whileFIG. 8 is a sectional view of the same along line C-C′ of FIG. 7, thatis, a cross-section of a semiconductor layer 1 which serves as an activelayer of the TFT. Embodiment 3 differs from embodiment 1 in that a firstshielding film 7 (area shaded with parallel lines having a positivegradient) is placed not only below a scan line 2 but below a data line3. Namely, in embodiment 3, the first light shielding film 7 is allowedto run below the scan line 2 and data line 3 to form a matrix. Throughthis arrangement, it is possible for the first light shielding film tofurther reduce a wiring resistance by being electrically connected to aconstant potential line such as a grounding potential line, and furtherto receive a constant potential even when wiring is disrupted by someforeign matters which by accident may fall onto the substrate duringtransportation for later processes. Accordingly, as the light shieldingfilm has a low wiring resistance and a redundant structure, it ispossible to obtain a display of high quality images free from cross-talkor the like.

[0154] In embodiment 3 like embodiment 1, below the channel regions 1 cof pixel TFT (areas shaded with parallel lines having a negativegradient), and below the scan line 2 and data line 3, is placed thelight shielding film 7 which is made of a metal film such as a tungstenfilm, a titanium film, a chromium film, a tantalum film or a molybdenumfilm, or a metal alloy film. Through this arrangement, it is possiblefor the scan line 2 and data line 3 (second light shielding film) to actas a shielding layer against incident light coming from the side wherean opposite substrate 31 resides, and for the first light shielding film7 to act as another shielding layer against light reflected from theback surface of substrate for the liquid crystal device. Thus light isprevented from directly impinging on the channel region 1 c and LDDregions 1 d and 1 e (or offset regions) of the pixel TFT. Thissuppresses a leakage current which would otherwise result from the TFTexposed to stray light. In embodiment 2, furthermore, all the sides ofthe pixel electrode 14, that is, the sides running lengthwise in FIG. 7are overlapped with data line 3, and the sides running crosswise areoverlapped with first light shielding film 7 below the scan line 2, andare separated from the adjacent pixel electrode 14 on the data line 3and the first light shielding film 7 beneath the scan line 2. Thisarrangement dispenses with the need for a black matrix 6. (third lightshielding film) placed on the opposite substrate 31. According to anexperiment done by the present inventors where a tungsten silicide filmwas used as the first light shielding film 7, and that film was soprepared as to have a thickness of about 2,000 Å. Then it was found outthat, with an optical density of 3 or more, the film showed a lightshielding activity as high as that which would be obtained if the devicehas a black matrix coated on the opposite substrate 31. This arrangementdispenses with the need for precise alignment of the black matrix 6 onthe opposite substrate 31 against the substrate for the liquid crystaldevice when the two kinds of substrates are bonded together, and thethus obtained liquid crystal devices show little variation in lighttransmittance.

[0155] In embodiment 3, description has been given assuming that thedata line 3 is placed like a matrix below the data line 3 and scan line2. Needless to say, however, as long as a wire consisting of the firstlight shielding film 7 is arranged at least below the scan line 2 as inembodiment 1, use of a black matrix on the opposite substrate can bedispensed with.

[0156] Embodiment 3 can also be produced through the same productionprocesses as used for the production of embodiment

[0157] (Embodiment 4)

[0158]FIGS. 9 and 10 represent the fourth preferred embodiment of asubstrate for liquid crystal device to which this invention has beenapplied. FIG. 9 is a plan view of pixels arrayed side by side, whileFIG. 10 is a sectional view of the same along line D-D′ of FIG. 9, thatis, a cross-section of a semiconductor layer 1 which serves as an activelayer of the TFT. Embodiment 4 differs from embodiment 3 in that a scanline 2 has a laminated structure consisting of a polysilicon layer 2 aand a metal film such as a tungsten film, a molybdenum film, etc., or ametal alloy film 2 b, and in that the first light shielding film 7(areas shaded with parallel lines having a positive gradient) is placeonly below a data line 3 (second light shielding film). In embodiment 3described above, as a polysilicon film constituting the scan line 2alone is present above the first light shielding film 7, the channelregion 1 c (areas shaded with parallel lines having a negative gradient)and LDD regions 1 d and 1 e (or offset regions) may be affected byincident light if they are too close to the pixel aperture. As a remedyto this problem, the scan line 2 is made of an opaque material such as ametal or a metal alloy. Namely, the sides of pixel electrode 14 runninglengthwise in FIG. 9 are shielded from light by the data line 3, whilethe sides running crosswise in FIG. 9 are shielded from light by thescan line 2. Accordingly, although, in embodiment 4, the extension fromthe first light shielding film 7 is placed below the data line 3, thesame may be placed only below the scan line 2 as in embodiment 1, or maybe wired like a matrix as in embodiment 3.

[0159] Incidentally, the metal or metal alloy film 2 b may be formed bysputtering, or may be formed after a metal film has been overlaidthrough vapor deposition on the polysilicon film 2 a, and the assemblybeen submitted to a heating treatment to produce a metal silicide film.Further, the scan line 2 may have a multi-layers structure with three ormore layers instead of double-layered structure as in the presentembodiment. For embodiment, the scan line may be formed after a closelyaffinitive polysilicon film 2 a is formed on a semiconductor layer 1,and a metal silicide layer 2 b having a low electric resistance and madeof tungsten silicide or the like is further placed over the assembly,and another polysilicon film is still further placed so as to cover theforegoing polysilicon film 2 a and metal silicide film 2 b. If the scanline 2 is composed of a metal or metal alloy film as described above, itwill not only prevent the entry of stray light but reduce a wiringresistance which would be considerable if the scan line is made solelyof polysilicon, and thus reduce delaying in signal transmission.

[0160] In embodiment 4 like embodiment 1, along the portion of data line(second light shielding film) which contacts with the pixel aperture oris very close to the same, the first light shielding film 7 placed belowhas a smaller width than does the data line 3 (second light shieldingfilm). This is because the data line 3 acts as a shield against incidentlight, and thus, prevents the first light shielding film 7 from beingexposed to light by having a larger width than that of the latter.

[0161] In embodiment 4, below the channel regions 1 c and LDD regions 1d and 1 e (or offset regions) of the pixel TFT, and below the data line3, is placed the light shielding film 7 which is made of a metalsilicide film such as tungsten silicide, and the scan line 2 has alaminar structure which contains a layer made of a metal or metalsilicide film which is impenetrable to light. Through this arrangement,it is possible for the scan line 2 and data line 3 to act as a shieldinglayer against incident light coming from the side where an oppositesubstrate 31 resides, and for the first light shielding film 7 to act asanother shielding layer against light reflected from the back surface ofsubstrate. Thus reflective light is prevented from directly impinging onthe channel region 1 c and LDD regions 1 d and 1 e (or offset regions)of the pixel TFT. This suppresses a leakage current which wouldotherwise result from the TFT exposed to stray light. In embodiment 4like embodiment 3, all the sides of the pixel electrode 14 areoverlapped with data line 3 and scan line 2 and are separated from theadjacent pixel electrode 14 on the data line 3 and scan line 2. Thisarrangement dispenses with the need for a black matrix 6 to be placed onthe opposite substrate 31 like embodiment 3.

[0162] Embodiment 4 can also be produced through the same productionprocesses as used for the production of embodiment 1.

[0163] (Embodiment 5)

[0164]FIG. 11 represents the fifth preferred embodiment of a substratefor liquid crystal device to which this invention has been applied. FIG.11 is a plan view of pixels arrayed side by side, and the cross-sectionalong line A-A′ of FIG. 11, or the sectional structure of asemiconductor layer 1 which acts as an active layer of the TFT is thesame with that shown in embodiment 1 (FIG. 2). Embodiment 5, instead ofplacing a scan line 2 below a data line 3 to obtain an extracapacitance, implements a capacitance line 16 in parallel with the scanline 2, and places an extension if from the semiconductor layer 1 belowthe capacitance line, to add an extra capacitance. The capacitance line16 is made of a polysilicon film which is produced through the sameprocess responsible for the production of the scan line 2, and is fixedto a constant potential such as a ground potential outside the displayarea. If the constant potential is obtained from a constant potentialline of a power source of an adjacent peripheral driving circuit, itwill be cost-effective because introduction of terminals speciallyprepared for the purpose would become unnecessary. Further, the gate ofthe pixel TFT is single. With a liquid crystal device incorporating asubstrate with such a capacitance line, it is necessary to let a blackmatrix applied onto an opposite substrate 31 have a large areas becausethe capacitance line 6 must be shielded from light. As there is aconsiderable distance between the pixel aperture along the capacitanceline 16 and the channel region 1 c (areas shaded with parallel lineshaving a negative gradient in FIG. 11) of the pixel TFT, adverse effectsdue to incident light from this side will be negligible. Accordingly,what is suspected of bringing adverse effects associated with incidentlight only involves the pixel aperture along the scan line 2. Thus, thisarrangement can halve a leakage current which would otherwise resultfrom incident light.

[0165] Embodiment 5 can also be produced through the same productionprocesses as used for the production of embodiment 1.

[0166] (Embodiment 6)

[0167]FIG. 12 represents the sixth preferred embodiment of a substratefor liquid crystal device to which this invention has been applied. FIG.12 is a plan view of pixels arrayed side by side, and the cross-sectionalong line B-B′ of FIG. 12, or the sectional structure of asemiconductor layer 1 which acts as an active layer of the TFT is thesame with that shown in embodiment 2 (FIG. 6). In embodiment 6, likeembodiment 5, a capacitance line 16 in parallel with a scan line 2 isimplemented, and an extension 1 f from the semiconductor layer 1 isimplemented below the capacitance line 16 to add an extra capacitance.The semiconductor layer 1 of the pixel TFT is shaped like a letter U,and a gate electrode has a dual gate formation. The capacitance line 16is made of a second polysilicon film which has been produced by the sameprocess responsible for the production of the scan line 2, and isconnected to a constant potential line such as a ground line outside thepixel region. As is evident from above, in embodiment 6, as thecapacitance line 16 must be shielded from light, it is necessary for ablack matrix placed on an opposite substrate 31 to have a sufficientlylarge area. As there is a considerable distance between the pixelaperture along the capacitance line 16 and the channel region 1 c (areasshaded with parallel lines having a negative gradient in FIG. 12) of thepixel TAT, adverse effects due to incident light from this side will benegligible. Accordingly, what is suspected of bringing adverse effectsassociated with incident light only involves the pixel aperture alongthe scan line 2. Thus, this arrangement can halve a leakage currentwhich would otherwise result from incident light.

[0168] Further, as the gate electrode of the pixel TFT has a dual gatestructure, the TFT comes to have a large resistance when turned off,which contributes to a further reduction of leakage current.Furthermore, in FIG. 12, like embodiment 2, only one out of two channelregions 1 c is placed below the data line 3 (second light shieldingfilm), but as long as one channel region 1 c is shielded from light bythe data line 3, a leakage current resulting from the TFT exposed tolight can be suppressed.

[0169] Embodiment 6 can also be produced through the same productionprocesses as used for the production of embodiment 1.

[0170] (Embodiment 7 and Determination of the Size of Light ShieldingFilms around a Data Line 3)

[0171]FIGS. 13 and 14 represent a representative embodiment of a pixelregion of the substrate for a liquid crystal device to which thisinvention has been applied and are modifications of Embodiment 5. InEmbodiment 7, a capacitance line 16 is placed below a pixel electrode 14with its part running obliquely, thereby not occluding the pixelaperture unnecessarily. FIG. 14 is a plan view of pixels arrayed side byside, and FIG. 14 is a sectional view of a structure cut along line E-E′of FIG. 13. A cross-section along line A-A′ of FIG. 13, or the sectionalstructure of a semiconductor layer 1 which acts as an active layer ofthe TFT has the same structure with that described above in embodiment 1(FIG. 2). In embodiment 7, the semiconductor layer 1 formed above afirst light shielding film 7 (areas shaded with parallel lines have apositive gradient in FIG. 13) with a first interlevel insulating film 11inserted in between is so prepared as to have at least the channelregion 1 c (areas shaded with parallel lines having a negative gradientin FIG. 13) and LDD regions 1 c and 1 e (or offset regions) totallycovered by the data line 3 (second light shielding film). In addition, ablack matrix 6 (third light shielding film) applied on an oppositesubstrate 31 which is bonded to a substrate for the liquid crystaldevice with a liquid crystal inserted in between, is so arranged as tocover at least the first light shielding film 7. At this stage it isnecessary to give an appropriate circuit pattern so that incident lightcoming from the side where the opposite substrate 31 resides maydirectly impinge on the first light shielding film 7.

[0172] To attain this, as shown in FIG. 14, the sizes of first lightshielding film 7, second light shielding film 3 (data line) and thirdlight shielding film 6 (black matrix on the opposite substrate) must bedetermined with respect to the width W of the channel region 1 c and LDDregions 1 d and 1 e (or offset regions). The widths of channel 1 c, andthe LDD regions 1 d and 1 e (or offset regions) maybe the same ordifferent. Desirably, the LDD regions 1 d and 1 e (or offset regions),and gate electrode (scan line) 2 must have the same width W, becausesuch arrangement is helpful for the attainment of pattern alignmentprecision, and stabilization of the pixel TFT performance. If the twoelements in question have to be altered in size, the LDD regions 1 d and1 e (or offset regions) where electrons are more easily excited may havea smaller width than the channel region 1 c, because this arrangementmore securely ensures a display of high quality images. In all theembodiments to which this invention has been applied, the sizes of lightshielding films are determined, assuming that the channel region 1 c andLDD regions 1 d and 1 e have the same width. In FIG. 14, the shortestdistances from the lateral edges of first light shielding film 7covering the channel region 1 c and LDD regions 1 d and 1 e (or offsetregions) when seen from the back surface of substrate 10, to the channelregion 1 c and LDD regions 1 d and 1 e (or offset regions) are definedas L1 and L1′. Then, a wiring pattern is preferably laid out to satisfythe following definition formula:

0.2 82 m≦L 1, L 1′≦4 μm  (1)

[0173] To achieve a high precision patterning of first light shieldingfilm 7 while maintaining a high pixel aperture of the liquid crystaldevice, desirably a wiring pattern is more preferably laid out tosatisfy the following definition formula:

0.8 μm≦L 1, L 1′≦2 μn  (2)

[0174] The values in the formula (2) are derived on the ground that, asthe first interlevel insulating film 11 has a thickness of about 8,000Å, light reflected from the back surface of substrate 10 must have anangle of 45° or more when measured at the lateral edge of first lightshielding film 7 and from the direction of incident light, in order toreach the channel region 1 c and LDD regions 1 d and 1 e (or offsetregions). Principally, incident light comes as parallel rays to adirection normal to the display area of the liquid crystal device, andhence it is quite unlikely for incident light to be reflected with anangle of 45° or more when measured at the lateral edge of first lightshielding film. Accordingly, as far as the formula (2) is satisfied,adverse effects due to reflective light can be practically ignored.

[0175] Next, the relationship between the first light shielding film 7and the second light shielding film (data line 3) will be defined. Toprevent the first light shielding film 7 against exposure to directincident light, it is necessary for the second light shielding film(data line 3) which is located above the first light shielding film 7 tohave a sufficient width. This is particularly true for this embodimentwhere the scan line 2 is absent, and LDD regions 1 d and 1 e are moresusceptible to incident light. The shortest distances from the lateraledges of the second light shielding film to the lateral edges of firstlight shielding film are defined as L2 and L2′. Then, a wiring patternis preferably laid out to satisfy the following definition formula:

0.2 μm≦L 2, L 2′  (3)

[0176] As the first and second interlevel insulating films 11 and 13have a summed thickness of about 15,000 Å, desirably a wiring pattern ismore preferably laid out to satisfy the following definition formula:

1.5 μm≦L 2, L 2′  (4)

[0177] These values are derived on the same ground as above involvingthe position of channel region 1 c and LDD regions 1 d and 1 e (oroffset regions) relative to the first light shielding film 7: unlessincident light had an angle of 45° or more when measured at the lateraledge of the second light shielding film (data line 3), it could notreach the surface of first light shielding film 7. However, as shown inFIG. 13, as the first light shielding film 7 placed below the channelregion 1 c extends along the scan line 2, the formulas (3) and (4) arenot satisfied at these overlapped areas. In spite of this, at leastlight shielding of channel region 1 c and LDD regions 1 d and 1 e (oroffset regions) poses no problem because they are safely covered by thescan line 2 and third light shielding film 6 (black matrix on theopposite substrate).

[0178] Next, the relationship between the second light shielding film(data line 3) and third light shielding film (black matrix 6 on theopposite substrate) must satisfy will be defined. Principally, as longas the second light shielding film (data line 3) has a sufficient lightshielding property, use of the third light shielding film (black matrix6 on the opposite substrate) will be unnecessary. Thus, it will bepossible to omit the placement of black matrix 6 (third light shieldingfilm) on the opposite substrate, as long as the scan line 2 is made ofan light shielding film, and all sides of the pixel electrode 14 aretotally covered by adjacent data lines 3 and scan lines 2. Eliminationof the black matrix 6 (third light shielding film) from the surface ofopposite substrate is further desirable in that it ensures a higherpixel aperture, because the black matrix, when wrongly aligned duringbonding of the opposite substrate 10 to the substrate for the liquidcrystal device, may cause the light transmission area of the pixel to betoo narrow. When the second light shielding film is formed of a metalfilm such as aluminum, or a metal alloy film which easily develops tinypin holes, it is necessary to add the third light shielding film (blackmatrix 6 on the opposite substrate) above the data line to preventleakage of light through those holes, and such device will result in aredundant structure. When a black matrix 6 (third light shielding film)must be introduced, desirably, the distances L3 and L3′ from the lateraledges of second light shielding films (data line 6) to the lateral edgesof third light shielding film 6 satisfy the following formula (5).

L 3, L 3′≦1 μm  (5)

[0179] This is because, as long as the formula (5) is satisfied, thepixel aperture is not hardly affected by the existence of the blackmatrix.

[0180] The channel width W heavily depends on the writing performance ofthe pixel TFT, but if the on/off ratio of the TFT can be sixth order ormore, the channel region with a shorter W gives a better result, becausethe channel region with a shorter width is less susceptible to straylight. Therefore, the channel region is so prepared as to satisfy:

0.2 μm≦W≦4 μm  (6)

[0181] or, more preferably:

0.2 μm≦W≦2 μm  (7)

[0182] Because, as long as above formulas are satisfied, the width ofthe data line 3 (second light shielding layer) can be narrowly formed,and thus a wider pixel aperture will be possible.

[0183] Embodiment 7 can also be produced through the same productionprocesses as used for the production of embodiment 1.

[0184] (Embodiment 8 and Determination of the Size of Light ShieldingFilm around a Scan Line 2)

[0185]FIGS. 19 and 20 represents the eighth preferred embodiment of asubstrate for liquid crystal device to which this invention has beenapplied. FIG. 19 is a plan view of pixels arrayed side by side, and FIG.20 is a sectional view of a structure along line F-F′ of FIG. 19. Inembodiment 8, a first light shielding film 7 (areas shaded with parallellines having a positive gradient in FIG. 19) as shown in embodiment 7takes a matrix form not only below the scan line 2 but below a data line3 and capacitance line 16. Through this arrangement it is possible forthe first light shielding film 7 to have a lowered electric resistance,and for the drain region 1 b of semiconductor layer 1 and first lightshielding film 7 to act as a capacitor with a first interlevelinsulating film 11 serving as a dielectric body, thereby to add an extracapacitance. Further, even if a black matrix 6 on an opposite substrate31 has flaws, the first light shielding film 7 can share the samefunction as that of the black matrix achieves, such defects as dottyflaws will be successfully reduced.

[0186] Next, in FIG. 23, the relationship between the first lightshielding film 7 and scan line 2 will be defined. The distance L4 fromthe lateral edge of first light shielding film below the scan line tothe lateral edge of scan line 2 close to the pixel aperture shouldsatisfy the following definition formula (8):

0.2 μm≦L 4  (8)

[0187] This is because, unless the first light shielding film 7 isdisplaced from the lateral edge of scan line 2 towards the center ofscan line 2, it will be directly exposed to incident light as long asthe lateral edge of scan line 2 and the side along pixel aperture arepositioned on the same side where the third light shielding film 6resides.

[0188] Next, the relationship between the first light shielding film 7below the capacitance line 16, and capacitance line 16 will be defined.The distance L5 from the lateral edge of first light shielding film 7below the capacitance line 16 to the lateral edge of capacitance line 16close to the pixel aperture should satisfy the following definitionformula (9):

0.2 μm>L 5  (9)

[0189] This is because, unless the first light shielding film 7 isdisplaced from the lateral edge of capacitance line 16 towards thecenter of capacitance line 16, it will be directly exposed to incidentlight as long as the lateral edge of the capacitance line 16 and theside along the pixel aperture are positioned on the same side where thethird light shielding film 6 resides.

[0190] Embodiment 8 can also be produced through the same productionprocesses as used for the production of Embodiment 1. It is needless tosay that the definition formulae (1) to (9) defined with respect toEmbodiments 7 and 8 can be applied to any substrate for a liquid crystaldevice and any liquid crystal device to which this invention has beenapplied.

[0191] In Embodiments 1 to 8, description has been given assuming thatthe first light shielding film 7 is formed directly on the surface of asubstrate 10 made of non-alkali glass or quartz, but it is possible toproduce the first light shielding film 7 for better flattening itssurface after a pattern of grooves corresponding with the layout offirst light shielding film 7 has been inscribed by etching on thesurface of a substrate 10, and the first light shielding film 7 beenapplied to fill those grooves. Further, the first light shielding film 7has its surface so treated as to prevent reflection. The reflectionprevention treatment may consist of oxidizing the surface of first lightshielding film made of a metal film or a metal alloy film such as metalsilicide by heating, to add an oxidized film, or of coating apolysilicon film by CVD on the surface of first light shielding film.

[0192] (Explanation of the Liquid Crystal Device)

[0193]FIG. 16(a) is a plan view illustration of the layout of the liquidcrystal device 30 which incorporates the substrate 32 for the liquidcrystal device. FIG. 16(b) is a sectional view of the same device alongH-H′ of FIG. 16(a). As shown in FIGS. 16(a) and 16(b), the oppositesubstrate 31 and the substrate for liquid crystal device 32 are bondedtogether with a sealing layer 36 comprising a gap material insertedbetween which fills a space formed between a display region 20 insideand data line driving circuit 50 and scan line driving circuit 60outside, such that the two substrates give a specified cell gap. Aliquid crystal 37 is enclosed in an inner space surrounded by thesealing layer 36. The sealing layer 36 has a break along its course, andthrough this break 38 (liquid crystal injection port) the liquid crystal37 has been injected. In preparation of the liquid crystal device 30,after the opposite substrate 31 and the substrate 32 for the liquidcrystal device have been bonded together, the inner region surrounded bythe sealing layer 36 is evacuated and the liquid crystal 37 is injected.After the liquid crystal 37 has been enclosed, the liquid crystalinjection port 38 is closed with a sealing material 39.

[0194] The sealing layer 36 may be made of an epoxy resin or variousphotosetting resins reactive to ultra-violet rays, and the gap materialto be combined therewith may include plastics or glass fibers in theform of cylinders with a diameter of about 2-6 μm or of balls. Theliquid crystal may include well-known TN (Twisted Nematic) liquidcrystals. Further, when the liquid crystal consists of apolymer-dispersed liquid crystal which is produced after liquid crystalparticles are allowed to disperse in a polymer, it dispenses with theneed for a alignment film and polarizer, and thus results in a liquidcrystal device with highly efficient light utilization.

[0195] In the liquid crystal device 30 of this embodiment, the oppositesubstrate 31 is smaller in size than the substrate for liquid crystaldevice 32, and thus, when the two substrates are bonded together, themargins of substrate for liquid crystal device 32 protrude outside fromthose of opposite substrate 31. Accordingly, the data line drivingcircuit 50 and scan line driving circuit 60 are arranged in a spacesurrounding the margins of opposite substrate 31, and this arrangementis helpful for preventing degradation of an alignment film made ofpolyimide or the like, and of liquid crystal 37 which may otherwiseresult from exposure to direct current components from peripheraldriving circuits. On the part of substrate for liquid crystal device 32protruding outward from the margins of opposite substrate 31, a lot ofinput/output terminals 40 are formed which are electrically connected toexternal ICs, and those terminals are connected to a flexible printedsubstrate by wire bonding or by ACF (Anisotropic Conductive Film)bonding.

[0196] Further, as shown in FIG. 18, in correspondence with pixelelectrodes 14 formed on the substrate for liquid crystal device 32,small lenses 80 are prepared in the form of a matrix on the oppositesubstrate 31, and as each small lens 80 can focus incident light on thepixel aperture region of a corresponding pixel electrode 14, it ispossible to greatly increase the contrast and brightness of images. Inaddition, as incident light is converged by the small lens 80,impingement of light upon the channel region 1 c and LDD regions 1 d and1 e (or offset regions) of pixel TFT 91 from an oblique angle can beeffectively prevented. Even if light converged by the small lens isreflected by the back surface of the substrate for liquid crystal device32, the substrate in question has the first light shielding film 7 soimplemented as to prevent the reflective light from impinging on thechannel region 1 c and LDD regions 1 d and 1 e (or offset regions) ofthe pixel TFT 91. Accordingly, a strong beam resulting from convergenceby the small lens does not affect the performance of the TFT, whichensures the production of a liquid crystal device with a display of highquality images. When small lenses 80 are implemented:, incident light ona pixel aperture is converged by the lens as indicated by dotted linesin FIG. 18, and thus it is possible to remove the black matrix 6 on theopposite substrate 31 without causing any extra troubles. Incidentally,although, in FIG. 18, small lenses 80 are placed on the oppositesubstrate 31 on the side facing the opposite electrode 33, they may beplaced on the opposite substrate 31 on the reverse side, andappropriately adjusted to focus incident light on the substrate forliquid crystal device 32 carrying respective pixel TFTs. In the latterarrangement as compared with the former, it is easier to adjust the cellgap. As shown in FIG. 18, small lenses made of a resin or the like arearrayed closely to each other with no interstices between, and bondedwith an adhesive onto a thin glass plate. Then, when the oppositeelectrode is formed on the thin glass plate, adjustment of the cell gapbecomes easy and a sufficiently efficient light utilization is achieved.

[0197] (Driving of the Liquid Crystal Device)

[0198]FIG. 15 shows the system composition of the liquid crystal device30 incorporating the substrate for the liquid crystal device ofembodiments 1 to 8. In this figure, 90 represents a pixel placed at eachintersection formed between the scan line 2 and data line 3, and eachpixel 90 consists of a pixel electrode 14 made of an ITO film and apixel TFT 91 which applies a voltage in response to an image signalsupplied to the data line 3. Pixels TFT 91 arranged in the same columnhave the gate electrodes connected to the same scan line 2, and thedrain regions 1 b to corresponding pixel electrodes 14. On the otherhand, pixels TFT 91 arranged in the same rows have the source regions 1a connected to the same data line 3. In this embodiment, transistorsconstituting the data line driving circuit 50 and scan line drivingcircuit 60 are composed of polysilicon TFTs each of which, like thepixel TFT 91, uses a polysilicon film as the semiconductor layer. Thetransistors constituting peripheral driving circuits (such as data linedriving circuit 50, scan line driving circuit 60, etc.) are composed ofCMOS type TFTs, and can be placed on the same substrate by the sameprocess as used for the production of pixel TFT 91.

[0199] In this embodiment, at least on one side (upper side in thefigure) of the display region 20 (region where pixels are arranged inthe form of a matrix) is placed a shift register 51 (to be referred toas X-shift register hereafter) which selects the data lines 3 one afteranother in order, and an X-buffer 53 which amplifies the output signalfrom X-shift register 51. Further, at least on one other side of thedisplay region 20 is placed another shift register 61 (to be referred toas Y-shift register hereafter) which drives the scan lines 2 one afteranother in order. Further, a Y-buffer 63 is added which amplifies theoutput signal from Y-shift register 61. Furthermore, on one end of eachdata line 3 is placed a sampling switch 52 (TFT) which is connected toan image signal line 54, 55 or 56 which transmits, for embodiment, imagesignals VID1-VID3 fed from outside, and those sampling switches are soarranged as to be switched on/off in order in response to samplingsignals provided by X-shift register 51. X-shift register 51, based onclock signals CLX1, counter clock signals CLX2 and start signals DX fedfrom outside, produces sampling signals X1, X2, X3, . . . , Xn whichallow an orderly activation of all data lines 3 in one horizontal scanperiod, and provides them to control terminals of sampling switches 52On the other hand, Y-shift register 61 is put into activation in synchwith clock signals CLY1, counter clock signals CLY2 and start signals DYfed from outside, and drives scan lines 2 of Y1, Y2, . . . Yn in order.

[0200] (Explanation of the Projection Type Display System)

[0201]FIG. 17 shows the constitution of a liquid crystal projector citedas an embodiment of projection type display device which incorporatesthe liquid crystal device of foregoing embodiments as a light valve.

[0202] In FIG. 17, 370 represents a light source such as a halogen lamp,371 a parabolic mirror, 372 a filter to cut off heat rays, 373, 375 and376 dichroic mirrors reflecting blue light, green light and red light,respectively, 374 and 377 reflective mirrors, 378, 379 and 380 lightvalves consisting of liquid crystal devices of the foregoingembodiments, and 383 a dichroic prism.

[0203] In the liquid crystal projector of this embodiment, white lightemitted from the light source 370 is converged by the mirror 371, passesthrough the heat-ray cutting-off filter 372 to be removed of its heatray component in the infra-red region, and impinges on the dichroicmirror system as visible rays. Then, firstly, blue rays (having awavelength of about 500 nm or shorter) are reflected by the dichroicmirror to reflect blue rays 373, and other rays (yellow rays) passthrough it. The blue light component thus reflected changes itsdirection after being reflected by the reflective mirror 374, and isincident on the blue-light modulating light valve 378.

[0204] On the other hand, light passing through the blue lightreflecting dichroic mirror 373 is incident on the green-light reflectingdichroic mirror 375 which reflects only a green light component (havinga wavelength of about 500-600 nm), and the remaining light component orred light passes through it The green light component reflected by thedichroic mirror 375 is incident on the green-light modulating lightvalve 379. Red light passing through the dichroic mirror 375 changes itsdirection after being deflected by the reflective mirrors 376 and 377and is incident on the red-light modulating light valve 380.

[0205] The light valves 378, 379 and 380 are driven by three primarycolor signals corresponding to blue, green and red componentsrespectively fed from an image signal processing circuit not illustratedhere. The light components incident on the respective light valves aremodulated there and combined by the dichroic prism 383. The dichroicmirror 383 is so constructed as to have the red-light reflective surface381 and blue-light reflective surface 382 intersect each other at rightangles. Then, a color image produced-after the light components havebeen combined by the dichroic mirror 383 is projected by the projectionlens 384 onto a screen as an enlarged image for display.

[0206] With the liquid crystal device incorporating this invention, as aleakage current generated from a pixel TFT 91 exposed to stray light iseffectively suppressed, such a liquid crystal projector as describedabove incorporating the liquid crystal devices as light valves can giveimages with a high contrast for display. Further, as the device inquestion has a high light shielding property, degradation of imagequality due to stray light will never result even when the light source370 gives bright light, or polarizing beam-splitters are insertedbetween the light source 370 and each or light valves 378, 379 and 380,to polarize the respective light components and thereby to improve lightutilization efficiency. Thus, a liquid crystal projector giving a brightdisplay will result. Furthermore, light reflected from the back surfaceof the substrate for liquid crystal device is practically negligible,and thus bonding of a non-glare polarizer or film onto reflectivesurfaces of the system becomes unnecessary, which contributes to alowering of production cost.

[0207] As shown in FIG. 17, for the system where triple light valvescorresponding to the red, green and blue light components and a dichroicprism are used in combination, this invention is particularlyadvantageous. Take, for embodiment, light reflected by the dichroicmirror 274. It passes through the light valve 378 and is combined withother light components by the dichroic prism 383. In this case, lightincident on the light valve 378 is modulated by 90° and is incident onthe projection lens. However, a very tiny portion of incident light onthe light valve 378 may leak outside and enter the light valve 380 onthe opposite side. Accordingly, to the light valve 380, comes not onlylight reflected from the dichroic mirror 377 (incident light advancingin the direction indicated by L in the figure) but possibly a portion oflight passing through the light valve 378 and then passing through thedichroic prism 382. Further, when light reflected by the dichroic mirror377 passes through the light valve 380 and is incident on the dichroicprism 382, a tiny portion thereof may be reflected (normal reflection)from the dichroic prism 383, and reenter the light valve 380. Asdiscussed above, the light valve is often exposed not only to light fromthe incoming path but to light from paths running in the oppositedirection. To cope with this situation, with this invention, as seenfrom the above description of the embodiments, light shielding films areimplemented around the pixel TFT 91 to shield it from light coming notonly along the incoming path but along paths in the opposite direction.In addition, the black matrix 6 having a larger size than the firstlight shielding film 7 is placed on the opposite substrate 31, toprevent light reflected from the first light shielding film 7 fromimpinging on the channel region 1 c and LDD regions 1 d and 1 e (oroffset regions) of pixel TFT 91, and thus the channel region 1 c and LDDregions 1 d and 1 e (or offset regions) in question can be safelyprotected against exposure to light coming not only from the incomingpath but from passes in the opposite direction (or from the backsurface). Therefore, this system ensures a great reduction of leakagecurrent which would otherwise result from the TFT being exposed to straylight.

[0208] Industrial Applicability

[0209] As detailed above, according to a substrate for liquid crystaldevice as described in Claim 1, with regard to light incident to achannel region, and junctions between the channel region andsource/drain regions, a first light shielding film shields light fromabove and a second light shielding film shields light from below. Thus,it is possible to reduce a leakage current which would otherwise resultfrom the TFT being exposed to light. Therefore, according to thisinvention, it is possible, for embodiment, to produce a substrate for aliquid crystal device with high performance active matrix pixels.Further, a substrate for the liquid crystal device to which thisinvention has been applied is most appropriate to be applied for theliquid crystal device, projector or the like.

What is claimed is:
 1. A substrate for a liquid crystal devicecomprising: a plurality of data lines formed on the substrate; aplurality of scan lines crossing the plurality of data lines, aplurality of thin film transistors connected to the plurality of datalines and the plurality scan lines; and a plurality of pixel electrodesconnected to the plurality of thin film transistors, wherein a firstlight shielding film is formed at least below channel region of the thinfilm transistors, and the junctions between the channel region andsource/drain regions, and a second light shielding film is formed abovethe channel region and its junctions between the channel region and thesource/drain regions.
 2. A substrate for a liquid crystal device asdescribed in claim 1, wherein the first light shielding film is a metalfilm selected from the group consisting of a tungsten film, a titaniumfilm, a chromium film, a tantalum film, a molybdenum film, or an alloyfilm thereof.
 3. A substrate for a liquid crystal device as described inclaims 1 or 2, wherein a first lead extending from the first lightshielding film is electrically connected to a constant potential lineoutside a pixel display region.
 4. A substrate for a liquid crystaldevice as described in any one of claims 1 to 3, wherein the first leadextending from the first light shielding film is formed along andbeneath the scan line.
 5. A substrate for a liquid crystal device asdescribed in any one of claims 1 to 4, wherein a width of the first leadextending from the first light shielding film is less than a width ofthe scan line formed above it.
 6. A substrate for a liquid crystaldevice as described in claim 5, wherein the first lead extending fromthe first light shielding film is covered by the scan line formed aboveit.
 7. A substrate for a liquid crystal device as described in any oneof claims 1 to 4, wherein a capacitance line which is formed on a samelayer as that of the scan line to add a capacitance to the pixel isplaced in parallel with the scan line, and has below it a second leadextending from the first light shielding film.
 8. A substrate for aliquid crystal device as described in any one of claims 1 to 7, whereina third lead extending from the first light shielding film is formedalong and below the data line.
 9. A substrate for a liquid crystaldevice as described in any one of claims 1 to 8, wherein the data linealso acts as a second light shielding film, and is made of a metal filmselected from the group consisting an aluminum film, a tungsten film, atitanium film, a chromium film, a tantalum film and a molybdenum film,or an alloy film thereof.
 10. A substrate for a liquid crystal device asdescribed in any one of claims 1 to 9, wherein a width of the third leadextending from the first light shielding film is less than a width ofthe data line.
 11. A substrate for a liquid crystal device as describedin any one of claims 1 to 10, wherein the channel region and thejunctions the channel region forms with the source/drain regions aredisposed below the data line, and the first light shielding filmdisposed below channel region and the junctions between the channelregion and the source/drain regions is covered by the data line at leaston the part underlying the channel region and the junctions between thechannel region and the source/drain regions.
 12. A substrate for aliquid crystal device as described in any one of claims 1 to 11, whereinLDD (lightly doped drain) regions are formed at the junctions of thechannel region with the source/drain regions.
 13. A substrate for aliquid crystal device as described in any one of claims 1 to 11, whereinthe junctions of the channel region with the source/drain regions areformed as offset regions.
 14. A substrate for a liquid crystal device asdescribed in any one of claims 1 to 13, wherein the scan line isselected from the group consisting of a metal film selected from atungsten film, a titanium film, a chromium film, a tantalum film and amolybdenum film, or a metal alloy film thereof.
 15. A substrate for aliquid crystal device as-described in any one of claims 1 to 13, whereina minimum distance L1 from the lateral edges of the first lightshielding film to the channel region is 0.2 μm≦L1≦4 μm.
 16. A substratefor a liquid crystal device as described in any one of claims 9 to 15,wherein a minimum distance L2 from the lateral edges of the second lightshielding film to the lateral edges of the first light shielding film is0.2 μm≦L2.
 17. A liquid crystal device as described in any one of claims1 to 16, wherein the substrate for the liquid crystal device and anopposite substrate with an opposite electrode are placed with aspecified interval in between, and that liquid crystal is injected intothe space between the substrate for the liquid crystal device and theopposite substrate.
 18. A liquid crystal device as described in claim17, wherein a third light shielding film is formed on the oppositesubstrate.
 19. A liquid crystal device as described in claim 17 or claim18, wherein the third light shielding film covers at least the firstlight shielding film.
 20. A liquid crystal device as described in anyone of claims 17 to 19, wherein small lenses are arranged in the form ofa matrix on the opposite substrate in correspondence with the pluralityof pixel electrodes placed on the substrate for the liquid crystaldisplay device.
 21. A projection type display device comprising a lightsource, a liquid crystal device as described in any one of claims 17 to20 to transmit or reflect light from the light source, after havingmodulated it, and a projection optical means which receives themodulated light from the liquid crystal device, and converges andenlarges it through projection.